Eclipse Forms: Rich UI for the Rich Client

Summary

Spice up your rich client with rich user experience using
Eclipse Forms. Written as a thin layer on top of SWT, Eclipse
Forms allow you to achieve the Web look in your desktop
applications without using the embedded browser. This allows you
to retain full control of the widgets in the UI and to maintain
portability across all operating systems Eclipse already runs on.
This article will take you from baby steps to advanced topics of
the rich user interface experience of Eclipse Forms.

By Dejan Glozic, IBM Canada Ltd.

January 16, 2005

The History (as we see it)

One of the fundamental features of the Eclipse platform is that
applications built on top of it look, feel and smell like genuine
native applications. Thanks to SWT, menus, windows, trees, tables,
buttons and other widgets all feel 'right' no matter what
OS or windowing system you are on. Being one of the first members
of the Eclipse team, I remember the days when I could get hours
of joy by playing with our prototype Eclipse code. Menus are
real. Tool bars are real. Combos, text, button, check boxes, radios are
all real. There is not a drawn widget in sight, all are native widgets.

For a long time, if your plug-ins contributed Eclipse user
interface artifacts, they would generally fall into the following
categories:

Editors

Views

Wizards

Dialogs

There are clear presentation rules for artifacts in these categories.
We are used to seeing trees and
tables in views, documents in editors and grids of simple widgets
like buttons and text fields in wizards and dialogs. These rules
are easy to follow and live by as long as your application is
similar in principle to Eclipse SDK.

The RCP (Rich Client Platform) concept in Eclipse 3.x represents
a fundamental broadening of the platform scope. It brought as a
corollary an effective explosion of the problem domains. You can now build Rich
client applications on top of Eclipse that have
little in common with IDEs. While generic workbench parts like
views and editors continue to work well, the widgets that are
populating these parts in IDEs (trees, tables, text editors, etc...)
may not be the best solution for this class of applications.
Available since Eclipse 3.0, Eclipse Forms are designed to offer
appealing alternatives.

Ironically, we developed Eclipse Forms as a solution for a
concrete problem in the Eclipse SDK long before RCP existed as a
concept. Developers of the PDE (Plug-in Development Environment)
working on the plug-in manifest editor did not feel happy with
following a Java editor paradigm of offering a color-coded,
context-assisted text editor for the plugin.xml file. There is
nothing wrong with Java editor in Eclipse by itself - in fact, it
is very powerful and ideally suited for the task. However, it was
designed for editing Java source files. In plug-in manifests, XML
was used as a format to describe data at a higher level of
abstraction. Editing XML by hand, even with color-coding and
context assist/code completion was not perceived as the correct
level of abstraction for the majority of users. In a plug-in
manifest, the syntax itself is not important (yet another thing to
learn). It is the data and what it represents that is important.

A good example of different ways of looking at markup
is HTML authoring tools. At the source code level, all we can see
are nested elements with the associated attributes. Although we see
the syntax, it is hard to visualize what it really represents. A
WYSIWYG view of the document can reveal a table, colors, some texts that span tables, images, etc.
Working with HTML files at this level of
abstraction is vastly more productive because syntax and markup are
hidden in the background (which is the reason why I am typing this
article on a WYSIWYG HTML authoring tool instead of hacking HTML
tags).

It is easy to understand what WYSIWYG concept means for HTML
documents. Since the HTML tags represent instructions for the web
browser on how to compose a document from text, presentation
attributes, hyperlinks and images, WYSIWYG in this context means
editing the document in its final form -- as close as possible to
the way it will appear in the browser. It was harder to figure out
what the alternative presentation would mean for the plug-in
manifest editor. Ultimately, the team made the following decisions:

Represent each section of the manifest in the way
most suitable for its nature. For example, vital information
like plug-in name, provider etc. can be easily edited in a text
field. Hierarchical structure of extensions maps nicely into the
tree widget etc.

Show sections of the manifest on separate editor pages,
regardless of their physical order in the source

Pages of the editor would keep a document feel and would be
able to host a mix of widgets, hyperlinks, images and text, and
offer scroll bars when content is too large for the page
size.

Figure 1: The Plug-in manifest editor as it
first appeared in Eclipse SDK 1.0. It offered a mixture SWT
widgets, hyperlinks and images that could scroll when there is not
enough space (as you would expect in a web browser). Note how all
the widgets have the 'flat' look that was selected for
less clutter and better fit in the document context.

The third point effectively spelled the birth of a plug-in that
now goes by the name of Eclipse Forms. Soon after release 1.0,
other developers wanted to replicate the rich user interface that
appeared in PDE multi-page editors. It was finally made available
as a plug-in with public APIs in Eclipse 3.0.

In the following text, we will show you what Eclipse Forms are
(and what they are not) and how to use them to create rich UI with
little effort.

Eclipse Forms Mission

Now that we know how Eclipse Forms came into being, it is useful
to describe their mission before going into details:

Eclipse Forms is anoptional
Rich Client plug-inbased on SWT and JFace
that provides the support for creatingportable web-style user interfacesacross all Eclipse UI categories.

Let's look at the mission statement in more detail:

Optional Rich Client plug-in - Eclipse Forms have
been rewritten in the 3.0 release to depend only on the
platform UI plug-in, and no longer rely on the PDE UI
plug-in. Despite they are not part of the minimal RCP
layer, you can add Eclipse Forms to any RCP application.

Based on SWT and JFace - Eclipse Forms
were not designed to compete with or offer an alternative to
SWT or JFace. The plug-in consists of a few carefully chosen
custom widgets, layouts and support classes to achieve the
desired effect when used with SWT and JFace.

Portable web-style user interfaces --
obviously, an Eclipse Form often looks like a web page.
The fact that each aspect of the form is
programmatically accessible at all times makes forms
powerful and attractive. Achieving the same flexibility in a
browser would require extensive DOM support and often
proprietary interactions. Eclipse Forms are portable,
being written on top of SWT and JFace.

Across all Eclipse UI categories -
Eclipse Forms breaks the mode by which certain classes of
widgets are be expected only in certain Eclipse UI categories
(editors, views, wizards, dialogs). An Eclipse form can
appear in any UI category, expanding development
possibilities. The UI developers can use the most appropriate
concept for the task.

Point cannot be underestimated. When
building interfaces in Eclipse Forms, you are using SWT. There is
no Eclipse Forms button, or Eclipse Forms tree widget as an
alternative to SWT widget. Instead, you are using Eclipse Forms
support to tweak subtly the existing widget set to achieve a richer
user experience.

Eclipse Forms make these rich user interfaces possible with the
following elements:

A concept of a 'form' that is suitable for
inclusion in content areas such as views and editors

A toolkit to manage colors, hyperlink groups and other
aspects of a form, and serve as a factory for many SWT
controls

A new layout manager that lays out controls in a manner
similar to an HTML table layout algorithm

A set of custom controls designed to fit in the form
(hyperlink, image hyperlink, scrollable composite, section)

A multi-page editor where most or all of the pages are forms
(e.g. PDE manifest editors)

Although nothing in the design of Eclipse Forms prevents you from
creating a form in a dialog, most of the usage scenarios have been
focused on using forms in views and editors, rather than dialog and
wizards. It is a matter of consistency -- having only a few
form-based dialogs or wizards would look very strange when all
other dialogs are 'normal'. Nevertheless, it is an
interesting area to explore in the future.

Baby steps

It is very easy to start using Eclipse Forms in your user
interfaces. You can start by adding a dependency on
org.eclipse.ui.forms plug-in. We will create an Eclipse view
that hosts a form and gradually fill in the content. Note that the
plug-in with all the source code used in this article is available
as a zip archive.

As you can see from this code snippet, it does not take much to
create a form. We start by creating an instance of a toolkit (
). We use the toolkit to create a scrolled
form using the provided composite as a parent. We set the
title of the form. We also make sure to transfer
focus to the form when needed and dispose the toolkit when the view
is disposed.

When we register the view using the class shown above and launch
the second Eclipse instance, the view should look like this:

Figure 2: A simple empty form in a view.
Making the view narrower will cause the form title to wrap. Once
there is no more space to fit the entire form, scroll bars will
appear.

Note that we have used scrolled form because we placed it in a
view that can be resized. In the more complex situations where a
form needs to be a child in a layout, a non-scrolled version is
available. In this case, we would have called
FormToolkit.createForm() instead and let the outmost
parent worry about scrolling the overall content.

Adding some content

Now that we have the form view running, we can start adding some
content to it. Eclipse forms have a body and we should create all
the content there:

The body of the form is the usable space below the form title.
Since this space is a SWT Composite, it can serve as a
parent for other widgets. In the code above, we
set the layout on the body, then create a
hyperlink. The hyperlink is one of the few custom widgets that
Eclipse Forms provide. The widget allows us to add a hyperlink
listener so that we can be notified when the user clicks on the
link.

The updated view should look like this:

Figure 3: A simple form with a
hyperlink

Note how hyperlink has a focus rectangle painted around it. Upon
view activation, focus is transferred to the form, which passes it
to the first control capable of accepting focus -- our link in this
case. With the keyboard focus in the link, simply pressing the
'Enter' key would activate the link.

Hyperlink Groups

Form toolkit has a hyperlink group object. Each created
hyperlink is added to this group object. Hyperlink groups serve
several roles. They define colors -- for normal, hover and active states -- for all links in the group. They change colors of the managed links based on their
state. They change underline style of the managed links based on
their state. They manage cursors and show busy cursor before link
listeners process the link activation, and revert it after.

You can change the default settings of the hyperlink group by
getting the object from the toolkit with
getHyperlinkGroup().

Creating common controls

One of the design goals of Eclipse Forms was to allow the
creation of common SWT controls in the editor/view content space.
Since form body is a normal composite, you can use any layout and
control you want inside it. However, remember that 'raw'
SWT controls come with a widget background. We will now create some
controls using their constructors:

We are now using two columns and creating a label, a text field
and a checkbox. The result is below:

Figure 4: A form with SWT controls created
directly using their constructors

What is wrong with this picture? The background of controls we
created directly matches the system dialog background, not the form
background. In addition, the text field looks fine because the
screen capture was taken on Windows XP. On other windowing systems,
it would look out of place due to the addition of a 3D border. To
fix this problem, we will create these controls using the
toolkit's factory methods instead:

Figure 5: A form with SWT controls created
using the form toolkit as a factory

Factory methods provided by the form toolkit are there for your
convenience. The toolkit is not all-inclusive --even for the SWT
widget set-- and definitely not for the custom controls that you may
have. A utility method FormToolkit.adapt(Control control,
boolean trackFocus, boolean trackKeyboard) should be used to
adapt an existing SWT control to fit into the form. Most of
the factory methods call adapt themselves.

Achieving the 'flat' look

One of the recognizable attributes of Eclipse Forms used in PDE
editors was the elegant 'flat' look of the controls. All
the controls used there were without 3D borders that look fine in
dialogs but less appealing in editors or views. This support is
built into the FormToolkit class. However, on some platform it
comes at a price of some custom rendering. For example, look at
this screen capture from PDE editor (version 2.1):

Figure 6: The flat look of Eclipse Forms
circa Eclipse 2.1

Controls like tables, text entries, combo box etc. are rendered
with a flat one-pixel border. These borders do not come from the
controls themselves (SWT.BORDER style is not used). Instead -- if
instructed -- the toolkit will add itself as a paint listener to
each control's parent, and draw borders around controls during
paint events. To make this happen, you need to call the toolkit
method paintBordersFor(parent) for each composite
where you created controls like text, tree, table etc. Note that
one call per parent is enough: there is no need to make a call for
each control of this type.

The Form toolkit knows which controls require a custom border.
However, you may create a new one that also needs a border that is
not on the list. You can give a hint to the toolkit by adding the
following code:

As you can see from the picture above, 'structural'
controls like trees and tables have a border style different from
text areas and you can choose which one to render for your control.
Note that this is not needed for controls created using
toolkit's factory methods.

Since
Eclipse 3.0 and on Windows XP, no border rendering is done when the
file javaw.exe.manifest file is present in the
Java virtual machine bin folder (I took all the screen shots in this article on Windows XP).
The presence of this file -- you can download
one from the
SWT home page -- instructs the toolkit to use XP skins for
native widgets. With XP skins, controls like text, table and tree
are already flat and there is no need to adjust the look. For
your code to be portable, you should always call
paintBordersFor(Composite), and let the toolkit choose
what to do depending on the windowing system.

Custom layouts

Eclipse Forms offer two new layouts in addition to the base SWT layouts.
These layouts extend the SWT Layout base class and
can be used on any SWT composite, but are typically used in
conjunction with Eclipse Forms.

TableWrapLayout

Now that we know how to populate the form, let's throw it a
curve. We will change the hyperlink text to be much longer:

link.setText("This is an example of a form that is much longer "+
"and will need to wrap.");

Let's see the result on screen:

Figure 7: A form laid out using
GridLayout

What happened? Remember that we are using
GridLayout. When it asked the link control to compute
its size, it gave it the size needed to render the text in one long
line. Although we instructed the control to wrap, it did not
matter because GridLayout requires that a control
return its size in isolation. The link itself -- as well as other
SWT controls like Label -- is capable of computing the
height given its width if you pass the width instead of
SWT.DEFAULT in computeSize, but
GridLayout is not passing the width as an argument.

What we need is a different layout algorithm that works more
like HTML tables. We want the content to try to fit in the provided
client area, and grow vertically to compensate. Eclipse Forms
provide an alternative layout for just such a purpose called
TableWrapLayout. There are many similarities between
GridLayout and TableWrapLayout. Both
organize parent's children in grids. Both have layout data
that instructs the layout how to treat each control. Both can
accept hints on which control should grab excess space etc.

However, they fundamentally differ in the approach to the
layout. TableWrapLayout starts with columns. It
computes minimal, preferred and maximum widths of each column and
uses this information to assign excess space. It also tries to be
fair when dividing space across columns so that there is no excess
wrapping of some controls.

It is possible to mix GridLayout and
TableWrapLayout but the branch of widgets tree where
GridLayout is used is the one where wrapping stops.
This is quite acceptable if you do not want it to wrap,
typically if the composite contains controls that cannot wrap
anyway, like text, buttons, trees etc... However, you should have an
un-broken path from the form body to each text control that needs
to wrap.

We used the same concepts that for GridData. Some of
the variables have different names (for example,
colspan and rowspan, align
and valign are taken from HTML TABLE attributes), but
you are doing the same thing -- creating a grid with two columns
where link and button span two columns. Since margins are the same
as in GridLayout, the result will look similar except
the link will now wrap:

Figure 8: A form laid out using
TableWrapLayout

One of the main differences between TableWrapLayout
and GridLayout is that with the former you should stop
thinking about the vertical dimension. In GridLayout,
you would typically let the 'rigid' controls assume their
natural positions and sizes and let 'flexible' controls
(text, tree and table) grab horizontal and/or vertical excess space.
In contrast, TableWrapLayout works top-down and when
it places all the controls, its work is complete. The concept of grabbing
excess space still exists in the horizontal dimension (as shown
above). However, vertically you can only choose to FILL the cell in
case it is taller than the control, or pick TOP, MIDDLE or BOTTOM
vertical alignment.

You may notice one thing that may seem contradictory to the
previous claim: TableWrapData still has
grabVertical variable. However, the variable is here
for a distinct purpose: when a fixed height control spans
multiple rows, its height will create a local condition where vertical
dimension is known, and controls in the spanned cells need to
divide the extra space between them.

In order to have good results with TableWrapLayout,
ensure that controls that can wrap have the appropriate style bit
(SWT.WRAP). Composite custom controls provided by
Eclipse Forms are wrap-enabled out of the box. This is achieved by
using internal layouts that implement ILayoutExtension
interface:

TableWrapLayout implements this interface itself,
which allows it to handle cases where composites with this layout
are children of the composite that is laid out. The additional two
methods allow it to compute the two extreme cases - the absolute
minimum width and the maximum width if all the controls are spread
as wide as possible. The difference between the two allows the
algorithm to distribute extra space fairly between columns to
minimize excess wrapping.

Let's take a closer look at space distribution. We will comment
the code we wrote so far in the view and replace it with the
following:

layout.numColumns = 3;
Label label;
TableWrapData td;
label = toolkit.createLabel(form.getBody(),
"Some text to put in the first column", SWT.WRAP);
label = toolkit.createLabel(form.getBody(),
"Some text to put in the second column and make it a bit "+
"longer so that we can see what happens with column "+
distribution. This text must be the longest so that it can "+
"get more space allocated to the columns it belongs to.",
SWT.WRAP);
td = new TableWrapData();
td.colspan = 2;
label.setLayoutData(td);
label = toolkit.createLabel(form.getBody(),
"This text will span two rows and should not grow the column.",
SWT.WRAP);
td = new TableWrapData();
td.rowspan = 2;
label.setLayoutData(td);
label = toolkit.createLabel(form.getBody(),
"This text goes into column 2 and consumes only one cell",
SWT.WRAP);
label.setLayoutData(new TableWrapData(TableWrapData.FILL_GRAB));
label = toolkit.createLabel(form.getBody(),
"This text goes into column 3 and consumes only one cell too",
SWT.WRAP);
label.setLayoutData(new TableWrapData(TableWrapData.FILL));
label = toolkit.createLabel(form.getBody(),
"This text goes into column 2 and consumes only one cell",
SWT.WRAP);
label.setLayoutData(new TableWrapData(TableWrapData.FILL_GRAB));
label = toolkit.createLabel(form.getBody(),
"This text goes into column 3 and consumes only one cell too",
SWT.WRAP);
label.setLayoutData(new TableWrapData(TableWrapData.FILL));
form.getBody().setBackground(form.getBody().getDisplay().
getSystemColor(SWT.COLOR_WIDGET_BACKGROUND));

This code creates a number of wrapping labels with text of
variable length. Some labels span columns, some span rows. To make
the test easier, we will set the form background to
widget background so that cells will be easy to spot. When we run
the example, we will get the following:

Figure 9: Excess space distribution in
TableWrapLayout

The key in space distribution is that the difference between
control minimum and maximum width is compared. The greater the
difference, the greater allocation of excess width will be for the
column. Excess width is any width greater than the width needed to
fit all the controls with their minimum widths taken into account.
Notice how column 3 is slightly wider than column 2 because text in
column 2 is somewhat longer. The overall goal is to avoid excessive
empty space in cells. If you want to read more about the theory
behind this layout algorithm, go to
W3C recommendations for HTML table auto-layout.

ColumnLayout

Another Eclipse Forms custom layout is a variation of SWT
RowLayout. If we configure RowLayout to
place children vertically -- in columns-- and to make all controls
have the same width within a column, we would get several columns,
depending on the width of controls. However, the last column would
typically not be completely filled -- depending on the number of
controls. When placed in a form, we would again get all the
controls in one column because RowLayout cannot do
'vertical' wrapping. If we use GridLayout
instead, we would have to choose the number of columns up front and
live with the choice.

There are situations in more complex forms where we want the
number of columns to be adaptive. In other words, we would like the
number to change depending on the width of the form -- use more
when possible, drop the number down as the width decreases. We
would also like to fill the form area equally like a newspaper
layout, with all the columns roughly the same height. All this can
be achieved with ColumnLayout.

Compared to TableWrapLayout,
ColumnLayout is much simpler. Hardly any configuration
is needed. The only choice you need to make is the range of columns
you want to have (default is 1 to 3). The following example shows a
form with a large number of sections (we will talk about sections
later) using ColumnLayout. Initially, there is enough
space to arrange the sections in two columns.
When we make the editor narrower, the layout arranges the sections in only one column:

Figure 10: Sections arranged in columns
using ColumnLayout. The layout started with two
columns but dropped to one when there was not enough space to fit
all the sections.

Complex controls

Eclipse Forms provide four complex custom controls that can help
you build rich looking UI: expandable composite, section, image
hyperlink and form text. Let's look closely at each of them.

Expandable composite

A common theme in sleek web pages is the ability to collapse a
portion of the page content using a toggle control. Eclipse Forms
offer such a control: ExpandableComposite.

The composite accepts a number of styles that control its
appearance and behavior. Style TREE_NODE will create the toggle
control used in a tree widget for expanding and collapsing nodes,
while TWISTIE will create a triangle-style toggle. Using EXPANDED
will create the control in the initial expanded state. If style
COMPACT is used, control will report width in the collapsed state
enough to fit in the title line only (i.e. when collapsed, it will
be as compact horizontally as possible). Finally, CLIENT_INDENT
will indent the client to align with the title (otherwise, client
will be aligned with the toggle control).

ExpandableComposite is responsible for rendering
the toggle control and the title. The client control to expand or
collapse must be a direct child of the expandable composite.

We needed to add expansion listener to the control and 'reflow'
the form on the state change. This is because expansion causes
changes in expandable composite size, but the change will not take
effect until the next time the parent is laid out (hence the need
to force it). In general, every time you do something that causes
the layout of the form to be invalid, you need to
'reflow' the form. 'Reflowing' the form will reposition the
controls according to the new sizes and update the scroll bars.

Our view now looks like this:

Figure 11: An example of the expandable
composite in the collapsed state

When you click on the '+' sign or on the title itself,
composite expands to reveal the client:

Figure 12: An example of the expandable
composite in the expanded state

The expandable composite uses
an internal layout implementing Eclipse Forms ILayoutExtension. Therefore you can add it to a parent that uses
TableWrapLayout, as we did in the example above.

Section

One of the most versatile custom controls in Eclipse Forms (and
seen in all PDE editors) is Section. It extends the
expandable composite and introduces the following concepts:

Separator - a separator control can be created below the
title

Description - an optional description can be added below the
title (and below the separator, if present)

Title bar - a title bar that encloses the section can be
painted behind the title (note that separator and title bar
should not be used simultaneously)

This time, we used the TWISTIE toggle style, added the
description and asked for the title bar to be painted. The view now
looks like this:

Figure 13: An expandable section with a
painted title bar and a description

Image hyperlink

Image hyperlink is a subclass of Hyperlink that
adds an image before the link text. This combination is so common
that it just made a lot of sense to make one control out of it and
save on widgets. The control can be used as an image link only
(when no text is set), or as a combination of link and image.
Images for normal, hover and active (selected) state can be set.

The following is an example of a rich user experience that uses
image hyperlinks:

Figure 14: A form taken from one of the
Eclipse Welcome pages (this is a fallback presentation used for the
cases when embedded browser creation fails)

Form text control

Using the combination of labels, hyperlinks, images and
TableWrapLayout, it is possible to create complex and
powerful forms. However, there are some things that are hard to do.
Consider the following example from the PDE manifest editor:

Figure 15: An example of a complex Eclipse
form that mixes wrapped text, images and hyperlinks

Notice how images, hyperlinks and text snippets are mixed
together. This is very hard using separate label and hyperlink
widgets. To remedy the problem, Eclipse Forms plug-in provides a
very rudimentary text control that can do the following:

Render plain wrapped text

Render plain text but convert any segment that starts with
http:// into a hyperlink on the fly

Render text with HTML-like tags (the form used in Figure 15
is using form text widgets in this mode)

In all the modes, form text control is capable of rendering
either a string or an input stream.

Figure 16: Form text control with a URL
automatically converted into a hyperlink

The URL has been converted into a link. The link is part of the
wrapped text - we did not have to create a separate
Hyperlink control and try to sandwich it between the
two labels.

Since form text control can render hyperlinks, it accepts the
same hyperlink listeners we used before. When created by the
toolkit, the form text will use the hyperlink settings from the
hyperlink group that belongs to the toolkit.

Parsing formatting markup

The most powerful use of the form text control is when
formatting tags are added to the text. The expected root tag is
'form'. It can have one or more children that can either
be <p> or <li>. Either of these can have normal text,
text between <b> or <span> tags, images and links.
Images are declared using <img href="image
key"/> (no content), while links are expressed using
<a href="href">text</a>.

Some of the tags mentioned above have additional attributes. Tag
<a> can accept nowrap='true' to block
the link from being wrapped into the new line. Tag <p> can
have attribute vspace='false' (true by
default) that adds additional space between paragraphs when set to
'true'. Tag <li> has more attributes:

style - can be "text", "bullet"
and "image" (default is "bullet")

value - not used for "bullet"; if style is
"text", the value will be rendered instead in place
of a bullet; if style is "image", value represents a
key in the image table of an image to be rendered in place of a
bullet

vspace - the same as for the 'p' tag.

indent - the number of pixels to indent text

bindent - the number of pixels to indent the bullet
(this number is independent from 'indent' - be
careful not to overlap them)

Tags that affect appearance of the normal text are <b>
(works as expected), and <span>. The latter allows you to
change font and/or color of the text within the tag. Finally, soft
line breaks can be added using <br/> tag.

Since Eclipse 3.1, it is possible to place an SWT control that is a
child of the form text in the markup. The new element
'control' accepts attribute 'href' that is a
key to the Control object set using
FormText.setControl(String key, Control control).
Optionally, attribute "fill" can be set to
true to make the control fill the entire width of the
text. Form text is not responsible for creating or disposing
controls, it only places them relative to the surrounding text.
Similar to <img>, vertical position of the control relative
to the surrounding text can be set using the 'align'
attribute.

How does all this work in practice? Let's make data text
that will use all of these tags together:

One common theme that can be observed is that the widget itself
is not responsible for loading images, fonts, resolving links or
colors. This is not a browser and it is much better to separate
concerns and simply assign images and colors managed elsewhere.
Both links and images simply have 'href' attribute to
reference them. For links, the value of this attribute will be
provided in the hyperlink event when listeners are notified. Images
need to be registered with the text control using the matching
'href' key. This way, the control does not need to worry
about loading the images - it has them in the hash table and can
render them immediately.

A similar approach has been used for colors and fonts. Colors
are already handled by the toolkit, so you can allocate as many as
you want using a unique key and RGB values by calling
toolkit.getColors().createColor(String key, RGB rgb).
What is left is to set all the colors referenced in the
'span' tag so that the control will be able to use them
during rendering.

When the code above is executed, the view looks like this:

Figure 17: Form text rendered from the XML
markup

If we expand the section and the expandable composite, and make
the window narrower, the form still holds and everything wraps
perfectly:

Figure 18: The sample view made taller and
narrower

Appropriate usage and limitations

Although the image above is very promising, it is very important
to contain excitement. A 'prime directive' of the form
text control is:

"Form text control is not, nor will it ever be, a web
browser"

It is very easy to spot limitations of the control. Tags within
list items or paragraphs cannot be nested. Bold is supported, but
not italic (although any font can be set and associated via the
'span' tag). Attributes for vertical alignment of text
with respect to images are missing. List support is decidedly low
level. There is no BIDI support.

Another important limitation to consider is performance. Form
text is neither a performance nor memory hog, but it was written to
be small and lean, not powerful. For that reason, it does not have
sophisticated painting routines, dirty region management etc. These
routines are cost-effective when the control owns the entire window
and must be scalable. In contrast, form text is best suited for
short snippets of tagged text that are mixed with other controls on
a form. This way, the control is one of several children in the
parent, allowing native dirty region management from the OS to
handle repaints. The best results in Eclipse forms are achieved
with a mixture that is similar to our example above.

Performance and painting of the form text widget has been improved
in Eclipse 3.1 and it can now handle more content without
performance degradation. For example, the new Help view is using
form text widget for rendering hundreds of images and search hits.
Nevertheless, the usage guidelines outline above still stand.

If you have a problem with the form text limitations, you should
consider alternatives:

If you need editing capability and text styling (with
different fonts and colors), use StyledText (used by
styled text editors like Java editor in Eclipse)

If you only need read-only support but have complex text
formatting needs, use
org.eclipse.swt.browser.Browser. Embedded web
browser works on most platforms and will give you full HTML
support.

What this widget is for is to provide for modest text formatting
in combination with TableWrapLayout and other controls
in a form. The power lies in the fact that you have full access to
every control - a kind of direct access that you can only achieve
in a browser if you use proprietary DOM access mechanisms. In
contrast, Eclipse Forms are portable - they run everywhere SWT
runs.

To conclude, use the form text widget:

when the UI you want to render is not very long with many
lines of text, hyperlinks and many images in complex layouts (use
embedded browser for that)

when you want to mix text, hyperlinks and images with SWT
controls like trees, tables and buttons.

when you want to run everywhere SWT runs

In contrast, use embedded web browser:

when the UI you want to render contains many lines of text,
hyperlinks and images arranged in complex layouts

when you do not need to mix SWT controls like trees and
tables with the text

when you want to use complex web technologies like
animation, sound or servlets/JSPs and/or render external web
pages in-place

when you want to achieve complex rendering effects like
transparency (all SWT widgets are opaque)

when you only need to ship on OS and/or window system
combinations where the embedded browser is fully supported

Advanced Topics

As usual in the real-world development, there is a chasm between
simple, happy examples that get you started and real code shipped
in products. This section covers aspects of Eclipse Forms that are
employed in production Eclipse code. You do not need to use
them right away, but chances are you will recognize their
advantages as your plug-in grows in complexity. In the following
text, we will address color and toolkit management, managed forms,
master/details block and multi-page editors.

Color And Toolkit Management

When using forms in a non-trivial way, it is important to share
as much as possible to conserve resources. For this reason, color
management should be separated from the toolkit when there is more
than one form to handle.

Of course, it is possible to create one toolkit per form, but
that is too wasteful if there are many forms. Instead:

Create one toolkit for all the forms that have the same life
cycle. For example, if creating a multi-page editor, create one
toolkit per editor and dispose it when editor is disposed. All
the pages in the editor should share this toolkit.

Create one color manager (FormColors) per
plug-in. When creating the toolkit, pass the color manager to
the toolkit. The toolkit will know that the colors are shared
and will not dispose them.

Use platform support for fonts and if possible, use
JFaceResources predefined fonts. Between default,
'banner' and 'header' fonts, you can
accomplish a lot. Using many fonts is very confusing for the
user, and if you do manage your own, you must ensure
alternatives across platforms. The JFace fonts are guaranteed
to work on all the platforms Eclipse ships on.

Dispose the color manager on plug-in shutdown (do not
assume that plug-in shutdown also means platform shutdown - in
Eclipse 3.x OSGi can uninstall your plug-in dynamically with
the platform still running).

Use form color manager to allocate all the colors needed by
the forms.

Managed forms

Managed forms are wrappers that add life cycle management and
notification to form members. A managed form is not a form by
itself. It has a form and accepts registration of
IFormPart element. For each IFormPart, it
manages events like dirty state, saving, commit, focus, selection
changes etc. In order to reach to the wrapped form widget, call the
'getfForm()' method.

Not every control on the form needs to be a form part. It is
better to group a number of controls and implement
IFormPart interface for the group. Section is a
natural group and Eclipse Form provides SectionPart
implementation. It implements the interface and contains a
Section instance (either created outside and passed
into the constructor, or created in the part itself).

Master/Details block

'Master/Details' is a pattern used throughout the UI world. It
consists of a list or a tree ('master') and a set of
properties ('details') driven by the selection in the
master. Eclipse Forms provide the implementation of the pattern as
a useful building block with the following properties:

While 'details' part is managed by the class
itself, the master part factory method is abstract and must be
implemented by the subclass

Master and details parts are children of a sash form and the
ratio of the form space allocated for each can be changed by
moving the sash.

As usual with a sash form, master and details parts can be
organized horizontally or vertically in the form.

The idea of master/details block is to create a tree or a table
section that fires the selection notification via the managed form.
If the details part can handle the selected object, it should
switch to the page for it and display properties. When building on
top of the provided master/details block, subclasses should:

Create the master part (the one that drives the details)

Contribute actions to the form tool bar (consumes
upper-right portion of the form in the title area)

Register details pages, one for each distinct input that can
arrive from the master part

We will show how this looks in practice using the source code
that accompanies this article. It creates a table for the master
part and hooks a few dummy objects of two distinct types. Two
details pages are registered to handle selections of these types.
Pages can contain any number of controls - they are created on
demand in the provided parent. The details area scrolls separately
from the master area.

This part can now be used anywhere, but in this example it was
placed inside an editor. Two distinct object types were used
(TypeOne and TypeTwo), and their classes
were used directly as keys (other mapping between details pages and
objects are possible). Details pages registered with the Details
part need to implement IDetailsPage interface.

The page is first initialized with the managed form to get
access to the toolkit and other objects. It is then asked to create
contents in the provided parent. It should also set focus on the
first control when asked, be able to refresh, commit, dispose and
react to the input changes. As long as objects selected in the
master part are of a compatible type, the page will stay visible
and inputChanged will be called.

Let's see how all this looks in practice:

Figure 19: An example of a master/details
block in horizontal orientation hosted in an editor

An instance of TypeOne object is selected in the
master part. The appropriate page for the type is loaded in the
details part. The page can contain any number of controls
introduced elsewhere in this article. The ratio of parts on the
page can be changed by scrolling the sash (visible when mouse goes
over the area between the parts). Also note two actions in the
upper-right corner of the form - this is the form tool bar. In this
case, two radio buttons were contributed to control orientation of
the part (horizontal or vertical).

If we change the orientation and select one of the
TypeTwo instances, we get into this state:

Figure 20: The same block in vertical
orientation and with a different element type selected

Orientation is now vertical, and a different details page is
shown for the type.

It is possible to register a detail page provider instead of
registering pages up front. This allows dynamic resolution of the
details page for the selected object. It is particularly important
for cases when different pages are needed for objects of the same
type depending on their states.

Multi-page form editors

It was a long way to get to this topic, yet PDE multi-page
editors were the first to spark interest in Eclipse Forms. Today,
multi-page editors still represent the most common use case of the
technology, even though it now starts to appear in other places.

Eclipse Forms are designed to work in a variety of
settings. For this reason, the plug-in cannot make assumptions on
the types of editor inputs your editor can receive. A number of
concepts employed in PDE UI cannot be used here because without
knowing about the editor input in more detail, it is hard to
provide a set of reusable classes. Nevertheless, Eclipse Forms
provide the basic support for multi-page editors, which you can
build on.

You should start building an Eclipse Forms multi-page editor by
extending FormEditor:

A very simple way to get started is to create pages and add them
as above. Each page needs to implement FormPage and
override createFormContent(IManagedForm managedForm).
Since there is already a managed form in each page,
you should create contents in that enclosed form and register
any form part that needs to be part of the managed life cycle.

In addition to form pages, you can add one or more text editors
as a raw source alternative to the GUI pages. For this, you should
call addPage(IEditorPart, IEditorInput
input) method in the super class.

Multi-page editor example

The source code that comes with this article contains an example
of a multi-page editor suitable for inclusion in an RCP application
because it does not have any dependencies on IDE plug-ins.

Once you launch another Eclipse application, customize the
perspective by checking the following checkbox in the test Eclipse
window:

Window>Customize Perspective...>Commands>Eclipse Forms
Article

This will add a menu to the menu bar called 'Form Article
Editors'. The menu contains only one action - 'Simple
Form Editor'. The action will open the editor. It has the
following pages:

Figure 21: A multi-page editor page with a
free-flowing text

The first page contains a page with a TableWrapLayout
and some sample content including a FormText widget. The
page content is free-form and will wrap and flow top to
bottom.

In contrast, the second page contains 'stretchy' controls -- two
table viewers -- that consume all the excess space on the page. Since
the controls can scroll themselves, a
GridLayout is used. Several PDE editor pages follow this pattern.

Figure 22: A multi-page editor page with
sections and tables.

The third page (Flow Page) was shown before in the
ColumnLayout section. It demonstrates how to
use this layout to adjust to the available space.
Master/Details sections are also shown above.

The last page shows how to embed aCTabFolder in
order to add another dimension to a form. In this particular example, the
actual content is not switched -- there is only one text control --
but its content is loaded from different objects depending on the
selected tab.

Figure 23: A multi-page editor page with
nested tabs

Recommended practices for Eclipse Forms multi-page editors

There are many ways to write a form-based
multi-page editor. It depends on the type of content you are
editing and the proficiency of your users. You can approach it in two ways:

If the typical users are using the editor infrequently, if raw
source is hard to edit by hand or complex, if your users are not
very technical, you should make COMPLETE pages capable of editing every aspect of the content without
the need to turn to the raw source. In this approach, a source editor
page is there only for occasional validation, rather than for
regular work. In that case, you can get away with a basic
text editor. The PDE extension point schema editor falls into
this group.

If your users are more technical, if they have no problem editing
the file by hand but would appreciate some help from time to
time, then consider providing a mixed experience -- make a good
source editor with all the add-ons like incremental outline,
context assist, syntax highlighting etc. Then, add complex
value-added functionality in form pages for actions that are hard to
achieve when editing raw source. We have learned from experience that it is
very hard to convince seasoned users to switch from source
editing if the value added is marginal or debatable. However,
when a function is only available in GUI pages and provides value and usability, it is adopted readily.

Creating a quality multi-page editor with mixed GUI and
source pages has its challenges. Accepting that users will switch
pages frequently requires a good model of the underlying content.
The model should be directly tied to the underlying document(s) to stay
in sync when users edit the raw text directly and
when they change it structurally through the forms pages. Also, do not
forget indirect changes caused by other workbench actions while
the editor is open.

For ideas on how to do this, see the source code of PDE editors
(org.eclipse.pde.ui plug-in) from the Eclipse CVS repository.

Conclusion

The goal of this article was to introduce you to a great way
to create powerful user interfaces in Eclipse 3.x. Eclipse Forms
is neither a competing widget toolkit that you need to choose over
SWT, nor does it make the embedded HTML browser widget obsolete.
Instead, it is a carefully written extension of SWT that allows you
to create surprisingly rich user interfaces in Eclipse while
retaining the portability of SWT. In simple cases, it can also be a
lightweight alternative to the SWT embedded browser widget. When
used within its limitations, Eclipse Forms can spice up your
applications and allow you to introduce a familiar Web-like metaphor.

Source Code

To run the example or view the source code for this article, go
through the following steps: